Trying to think about how this would be visible on the user-end. Would we be able to see the recipient as "my.mail@gmail" and "m.y.m.a.i.l.@gmail" instead of the catch-all "mymail" handle?

Mykolab handles it as prefix+user@. Not sure how gmail does it exactly.

You can enter a rule in GMail parsing those special addresses (m.y.m.a.i.l@gmail.com or mymail+SPAM@gmail.com directly tagged as spam for example). If you look at the details of the mail, you can see it is addressed to those special handles.

5 millions gmail addresses were leaked recently. Along with 5 millions passwords. May be that the list made its way to spammers hands before being post publicly.